feat!: adds async iterator for custom promises

NODE-2590

Author: Thomas Reggi

src/cursor/cursor.ts

@@ -9,6 +9,7 @@ import { CountOperation, CountOptions } from '../operations/count';
 import { ReadPreference, ReadPreferenceLike } from '../read_preference';
 import { Callback, emitDeprecatedOptionWarning, maybePromise, MongoDBNamespace } from '../utils';
 import { Sort, SortDirection, formatSort } from '../sort';
+import { PromiseProvider } from '../promise_provider';
 import type { OperationTime, ResumeToken } from '../change_stream';
 import type { CloseOptions } from '../cmap/connection_pool';
 import type { CollationOptions } from '../cmap/wire_protocol/write_command';
@@ -1227,7 +1228,7 @@ export class Cursor<
   }
 
   /** Close the cursor, sending a KillCursor command and emitting close. */
-  close(): void;
+  close(): Promise<void>;
   close(callback: Callback): void;
   close(options: CursorCloseOptions): Promise<void>;
   close(options: CursorCloseOptions, callback: Callback): void;
@@ -1320,6 +1321,17 @@ export class Cursor<
     return this.logger;
   }
 
+  [Symbol.asyncIterator](): AsyncIterator<Document> {
+    const Promise = PromiseProvider.get();
+    return {
+      next: () => {
+        if (this.isClosed()) {
+          return Promise.resolve({ value: null, done: true });
+        }
+        return this.next().then(value => ({ value, done: value === null }));
+      }
+    };
+  }
   // Internal methods
 
   /** @internal */

src/mongo_client.ts

@@ -273,6 +273,9 @@ export class MongoClient extends EventEmitter implements OperationParent {
 
     if (options && options.promiseLibrary) {
       PromiseProvider.set(options.promiseLibrary);
+      // TODO NODE-2530: this will go away when client options are sorted out
+      // NOTE: need this to prevent deprecation notice from being inherited in Db, Collection
+      delete options.promiseLibrary;
     }
 
     // The internal state
@@ -440,10 +443,6 @@ export class MongoClient extends EventEmitter implements OperationParent {
     if (typeof options === 'function') (callback = options), (options = {});
     options = options || {};
 
-    if (options && options.promiseLibrary) {
-      PromiseProvider.set(options.promiseLibrary);
-    }
-
     // Create client
     const mongoClient = new MongoClient(url, options);
     // Execute the connect method

test/node-next/es2018/cursor_async_iterator.test.js

@@ -1,91 +1,134 @@
 'use strict';
 
 const { expect } = require('chai');
+const Sinon = require('sinon');
 
-// TODO: unskip as part of NODE-2590
-describe.skip('Cursor Async Iterator Tests', function () {
-  let client, collection;
-  before(async function () {
-    client = this.configuration.newClient();
+describe('Cursor Async Iterator Tests', function () {
+  context('default promise library', function () {
+    let client, collection;
+    before(async function () {
+      client = this.configuration.newClient();
 
-    await client.connect();
-    const docs = Array.from({ length: 1000 }).map((_, index) => ({ foo: index, bar: 1 }));
+      await client.connect();
+      const docs = Array.from({ length: 1000 }).map((_, index) => ({ foo: index, bar: 1 }));
 
-    collection = client.db(this.configuration.db).collection('async_cursor_tests');
+      collection = client.db(this.configuration.db).collection('async_cursor_tests');
 
-    await collection.deleteMany({});
-    await collection.insertMany(docs);
-    await client.close();
-  });
+      await collection.deleteMany({});
+      await collection.insertMany(docs);
+      await client.close();
+    });
 
-  beforeEach(async function () {
-    client = this.configuration.newClient();
-    await client.connect();
-    collection = client.db(this.configuration.db).collection('async_cursor_tests');
-  });
+    beforeEach(async function () {
+      client = this.configuration.newClient();
+      await client.connect();
+      collection = client.db(this.configuration.db).collection('async_cursor_tests');
+    });
+
+    afterEach(() => client.close());
 
-  afterEach(() => client.close());
+    it('should be able to use a for-await loop on a find command cursor', {
+      metadata: { requires: { node: '>=10.5.0' } },
+      test: async function () {
+        const cursor = collection.find({ bar: 1 });
 
-  it('should be able to use a for-await loop on a find command cursor', {
-    metadata: { requires: { node: '>=10.5.0' } },
-    test: async function () {
-      const cursor = collection.find({ bar: 1 });
+        let counter = 0;
+        for await (const doc of cursor) {
+          expect(doc).to.have.property('bar', 1);
+          counter += 1;
+        }
 
-      let counter = 0;
-      for await (const doc of cursor) {
-        expect(doc).to.have.property('bar', 1);
-        counter += 1;
+        expect(counter).to.equal(1000);
       }
+    });
 
-      expect(counter).to.equal(1000);
-    }
-  });
+    it('should be able to use a for-await loop on an aggregation cursor', {
+      metadata: { requires: { node: '>=10.5.0' } },
+      test: async function () {
+        const cursor = collection.aggregate([{ $match: { bar: 1 } }]);
 
-  it('should be able to use a for-await loop on an aggregation cursor', {
-    metadata: { requires: { node: '>=10.5.0' } },
-    test: async function () {
-      const cursor = collection.aggregate([{ $match: { bar: 1 } }]);
+        let counter = 0;
+        for await (const doc of cursor) {
+          expect(doc).to.have.property('bar', 1);
+          counter += 1;
+        }
 
-      let counter = 0;
-      for await (const doc of cursor) {
-        expect(doc).to.have.property('bar', 1);
-        counter += 1;
+        expect(counter).to.equal(1000);
       }
-
-      expect(counter).to.equal(1000);
-    }
-  });
-
-  it('should be able to use a for-await loop on a command cursor', {
-    metadata: { requires: { node: '>=10.5.0', mongodb: '>=3.0.0' } },
-    test: async function () {
-      const cursor1 = collection.listIndexes();
-      const cursor2 = collection.listIndexes();
-
-      const indexes = await cursor1.toArray();
-      let counter = 0;
-      for await (const doc of cursor2) {
-        expect(doc).to.exist;
-        counter += 1;
+    });
+
+    it('should be able to use a for-await loop on a command cursor', {
+      metadata: { requires: { node: '>=10.5.0', mongodb: '>=3.0.0' } },
+      test: async function () {
+        const cursor1 = collection.listIndexes();
+        const cursor2 = collection.listIndexes();
+
+        const indexes = await cursor1.toArray();
+        let counter = 0;
+        for await (const doc of cursor2) {
+          expect(doc).to.exist;
+          counter += 1;
+        }
+
+        expect(counter).to.equal(indexes.length);
       }
+    });
 
-      expect(counter).to.equal(indexes.length);
-    }
-  });
+    it('should properly stop when cursor is closed', {
+      metadata: { requires: { node: '>=10.5.0' } },
+      test: async function () {
+        const cursor = collection.find();
 
-  it('should properly stop when cursor is closed', {
-    metadata: { requires: { node: '>=10.5.0' } },
-    test: async function () {
-      const cursor = collection.find();
+        let count = 0;
+        for await (const doc of cursor) {
+          expect(doc).to.exist;
+          count++;
+          await cursor.close();
+        }
 
-      let count = 0;
-      for await (const doc of cursor) {
-        expect(doc).to.exist;
-        count++;
-        await cursor.close();
+        expect(count).to.equal(1);
       }
-
-      expect(count).to.equal(1);
-    }
+    });
+  });
+  context('custom promise library', () => {
+    let client, collection, promiseSpy;
+    before(async function () {
+      class CustomPromise extends Promise {}
+      promiseSpy = Sinon.spy(CustomPromise.prototype, 'then');
+      client = this.configuration.newClient({}, { promiseLibrary: CustomPromise });
+
+      await client.connect();
+      const docs = Array.from({ length: 1 }).map((_, index) => ({ foo: index, bar: 1 }));
+
+      collection = client.db(this.configuration.db).collection('async_cursor_tests');
+
+      await collection.deleteMany({});
+      await collection.insertMany(docs);
+      await client.close();
+    });
+
+    beforeEach(async function () {
+      client = this.configuration.newClient();
+      await client.connect();
+      collection = client.db(this.configuration.db).collection('async_cursor_tests');
+    });
+
+    afterEach(() => {
+      promiseSpy.restore();
+      return client.close();
+    });
+
+    it('should properly use custom promise', {
+      metadata: { requires: { node: '>=10.5.0' } },
+      test: async function () {
+        const cursor = collection.find();
+        const countBeforeIteration = promiseSpy.callCount;
+        for await (const doc of cursor) {
+          expect(doc).to.exist;
+        }
+        expect(countBeforeIteration).to.not.equal(promiseSpy.callCount);
+        expect(promiseSpy.called).to.equal(true);
+      }
+    });
   });
 });